Hydroformylation is the reaction of an unsaturated compound with hydrogen and carbon monoxide to give an aldehyde compound in the presence of a catalyst system.
Such a process is described in WO-A-9518089. WO-A-9518089 describes the preparation of methyl-5-formylvalerate through hydroformylation of methyl-3-pentenoate in the presence of a catalyst system containing rhodium and a multidentate organic phosohite ligand.
A drawback of this process is that the multidentate phosphite ligand proves to be sensitive to degradation in the presence of traces of oxygen or other oxidising compounds, for example hydroperoxide compounds, which may be present during the reaction. Oxygen may for example leak into a continuously operating process. Degradation of the ligand is a disadvantage because fresh ligand has to be added to the system to ensure that the activity and selectivity to aldehyde compounds of the reaction remain at the required level for a longer period. Adding such large amounts of fresh ligand per kg of aldehyde product is not attractive from an economic viewpoint, in view of the relatively high cost price of this type of phosphite ligand and hence of the aldehyde product.
The object of this invention is a process in which, in the presence of traces of oxygen, less phosphite ligand is consumed per kg of aldehyde product than in the process according to the state of the art.
This object is achieved in that a monodentate phosphine is present.